Caffeine- and aminophylline-induced seizures

The epileptogenicity of caffeine and aminophylline was studied in rats. Intraperitoneal administration of caffeine produced an immediate excitation and seizures followed by an encephalopathy. A progression from encephalopathy to seizures was observed following aminophylline administration. During the development of behavioral seizures, the EEGs showed a progression from fast activity isolated or bursts of spikes and/or sharp waves to full-blown epileptiform discharges. A wide spectrum of cardiac arrhythmias was observed during and following the seizures. Epileptiform activities ranging from isolated or bursts of spikes and/or sharp waves to continuous epileptiform discharges were observed following local application of the drugs to the cerebral cortex.

Adenosine receptor antagonism accounts for the seizure-prolonging effects of aminophylline

The mechanism of action of aminophylline in prolonging seizures was tested in amygdala-kindled rats. Aminophylline prolonged the afterdischarge duration of kindled seizures. This seizure-prolonging action of aminophylline was strongly antagonized by the adenosine A1 agonist cyclohexyladenosine and partially antagonized by the benzodiazepine partial agonist RO 15-1788. However, the specific benzodiazepine antagonist CGS 8216 did not affect the seizure-prolonging action of aminophylline. Also, the potent anticonvulsant effect of diazepam on kindled seizures, which was completely antagonized by CGS 8216, was unaffected by aminophylline. Furthermore, a range of benzodiazepine inverse agonists, GABA antagonists, phosphodiesterase inhibitors and xanthines did not prolong afterdischarge durations. These results demonstrate that the seizure-prolonging action of aminophylline is due to block of A1 adenosine receptors since it is prevented by adenosine A1 agonists.

Inhibition of aminophylline-induced convulsions in mice by antiepileptic drugs and other agents

Common antiepileptic drugs and agents affecting different neurotransmitter systems were studied against aminophylline (280 mg/kg i.p.)-induced convulsions in mice. All drugs and agents were administered i.p. Diazepam and phenobarbital antagonized the whole seizure pattern and the respective ED50 values for the clonic phase were 3.5 and 62 mg/kg. Valproate at 500 mg/kg protected fewer than 50% of mice against the clonic phase. The remaining antiepileptics (acetazolamide, up to 1,000 mg/kg; carbamazepine and diphenylhydantoin, up to 50 mg/kg; ethosuximide, 500 mg/kg and trimethadione, 400 mg/kg) were totally ineffective in this respect. Propranolol (up to 20 mg/kg), baclofen (20 mg/kg), gamma-hydroxybutyric acid (300 mg/kg), aminooxyacetic acid (20 mg/kg), clonidine (up to 0.2 mg/kg), ketamine (30 mg/kg), atropine (20 mg/kg), papaverine (50 mg/kg) and L-phenylisopropyladenosine (2 mg/kg) did not affect the clonic phase either. Only antagonists of N-methyl-D-aspartic acid excitation, 2-amino-5-phosphonopentanoic acid and 2-amino-7-phosphonoheptanoic acid afforded protection against aminophylline-induced clonic seizure activity. The results show that aminophylline convulsions are relatively resistant to antiepileptic drugs and suggest that antagonists of excitatory transmission are potential antiaminophylline drugs.

Enhancement of cardiotoxic effects of beta-adrenergic bronchodilators by aminophylline in experimental animals

To examine the cardiotoxic interaction between beta-adrenergic bronchodilators and theophylline, we tested the effects of isoproterenol or bitolterol alone and in combinations with aminophylline in experimental animals, both electrocardiographically and histologically. The sc LD50 values for isoproterenol in 4- to 5-month-old, 500-600 g (heavy) and 1.5- to 2-month-old, 150-200 g (small) male Sprague-Dawley rats were 0.6 mg/kg and 1300 mg/kg, respectively, and values for bitolterol were 4 mg/kg and greater than 1800 mg/kg, respectively. Results of the electrocardiographic studies in heavy rats, using the calculated LD20 dosage of isoproterenol with or without pretreatment of aminophylline, demonstrated that both mortality and the arrhythmia-inducing effect of isoproterenol were significantly potentiated by aminophylline but only mortality was increased in small rats. Aminophylline also potentiated the electrocardiographic effects of 1/40 of the LD50 dosage of isoproterenol in heavy rats but did not enhance the effects of bitolterol at this dose level. Potentiation of the arrhythmogenic effect of isoproterenol was also observed in rabbits. The severity of the myocardial lesions produced by isoproterenol or bitolterol in heavy rats was significantly enhanced by aminophylline. The heavy rat appears to be a sensitive model for studying the interaction of these classes of drugs.

Coronary vascular lesions in dogs treated with phosphodiesterase III inhibitors

A treatment-related coronary arteriopathy has been observed in the dog following the oral or intravenous administration of 4 potent phosphodiesterase type III inhibiting inodilators at high multiples of their ED50 for periods from 1 day to 6 months. A fifth compound of a similar pharmacological class exhibited limiting toxicity at low multiples of its ED50 and this compound failed to induce coronary arterial lesions. The earliest treatment-related findings observed were medial hemorrhage and necrosis with focal breaks in the internal elastic lamina. Later changes, observed from day 9 onwards, included intimal thickening consisting of smooth muscle proliferation with a mucoid ground substance, variable and inconsistent inflammatory changes involving one or more arterial tunics and adventitial hemorrhage, fibrosis and neovascularization. The changes were restricted to the coronary arteries including the extramural and intramural branches. The distribution of lesions varied from widespread, multifocal involvement of both coronary arterial systems to focal lesions with no obvious site of predilection. Induction of this lesion may involve changes in coronary flow and pressure as a result of an exaggerated pharmacological response to this class of compound. The susceptibility of other species (rat, cynomolgus monkey, or pig) to this effect has been investigated with no treatment-related arteriopathy being observed.

Neonatal apnea, xanthines, and necrotizing enterocolitis

This study evaluates the relationship of xanthine treatment of premature apnea and NEC in a bowel ischemia model. The superior mesenteric artery was occluded for 1.0 minute in 82 wheanling rats. Group I (n = 41) were untreated controls. Group II (n = 21) received aminophylline (AMPH) 40 mg/kg I.P., 4 hr and immediately prior to clamping. Animals were evaluated for bowel infarction, perforation, and mortality at 7 days. In 20 additional rats (10 per group) bowel was evaluated by scanning electron microscopy (EM) at timed intervals (5 and 30 min). Ischemic bowel occurred in 25 of 41 (60%) controls (18 (43%) with necrosis; 7 (17%) with perforations) and 19 of 21 (90%) rats with AMPH (15 (70%) had necrosis; 4 (19%) perforations). Mortality was 60% (controls) and 90% (AMPH) respectively (p less than .05). On EM, AMPH enhanced bacterial overgrowth however actual mucosal damage appeared similar. Following ischemia, AMPH has an adverse effect on the bowel. Use of AMPH in prematures at risk for NEC is questioned.

Possible role of free radicals in theophylline-induced seizures in mice

Theophylline is a methylxanthine bronchodilator with a narrow therapeutic index and is prone to induce seizures, the mechanisms for which are not clearly defined. Free radicals have considerable neurotoxic potential and the present study evaluated the possible involvement of these bioactive moieties in aminophylline-induced seizures in mice. Aminophylline (50-250 mg/kg) induced convulsions and mortality in mice in a dose-dependent manner. The anti-oxidants, melatonin (25-100 mg/kg) and N-actylcysteine (100 and 200 mg/kg) attenuated aminophylline seizures and mortality. Similar antagonism of aminophylline seizures was also observed after pretreatments with nitric oxide (NO) synthase inhibitors, L-NAME (3 and 10 mg/kg) and 7-nitroindazole (10 and 30 mg/kg). Further, combined treatment with otherwise sub-effective doses of melatonin and L-NAME or 7-nitroindazole produced marked protective effects against these seizures. Aminophylline-induced seizures enhanced malondialdehyde (MDA) concentrations and NO metabolite (NOx) levels in the brain homogenates of mice, and these were attenuated by melatonin and L-NAME pretreatments. The results are suggestive of the possible involvement of free radicals (reactive oxygen and reactive nitrogen species) in the convulsiogenic effects of aminophylline.

NG-nitro-L-arginine, a nitric oxide synthase inhibitor, and seizure susceptibility in four seizure models in mice

Nitric oxide may be involved in seizure phenomena even though data often seem to be contradictory. This prompted us to study the influence of nitric oxide upon electrically and chemically induced seizures. The effects of nitric oxide synthase inhibitor, NG-nitro-L-arginine (NNA), on pentylenetetrazol-, aminooxyacetic acid-, aminophylline-induced seizures or electroconvulsive shock were evaluated. NNA was applied at 1, 10 and 40 mg/ kg 0.5 and 2.0 h before chemical seizures and at 1 and 40 mg/kg 0.5 and 2.0 h prior to electroconvulsions. The nitric oxide synthase inhibitor (up to 40 mg/ kg) did not affect the susceptibility of mice to pentylenetetrazol, amino-oxyacetic acid or electroconvulsions. However, NNA significantly enhanced the convulsive properties of aminophylline when applied at 40 mg/kg, 0.5 h before the test. The CD50 value for aminophylline-induced clonus and tonus/ mortality was decreased from 233 to 191 and from 242 to 212 mg/kg, respectively. However, this pretreatment also led to a significant increase in the plasma levels of theophylline. Our results suggest that differential effects of NNA on chemically-induced convulsions might in some cases be associated with a pharmacokinetic interaction.

Zebrafish on a chip: a novel platform for real-time monitoring of drug-induced developmental toxicity

Pharmaceutical safety testing requires a cheap, fast and highly efficient platform for real-time evaluation of drug toxicity and secondary effects. In this study, we have developed a microfluidic system for phenotype-based evaluation of toxic and teratogenic effects of drugs using zebrafish (Danio rerio) embryos and larvae as the model organism. The microfluidic chip is composed of two independent functional units, enabling the assessment of zebrafish embryos and larvae. Each unit consists of a fluidic concentration gradient generator and a row of seven culture chambers to accommodate zebrafish. To test the accuracy of this new chip platform, we examined the toxicity and teratogenicity of an anti-asthmatic agent-aminophylline (Apl) on 210 embryos and 210 larvae (10 individuals per chamber). The effect of Apl on zebrafish embryonic development was quantitatively assessed by recording a series of physiological indicators such as heart rate, survival rate, body length and hatch rate. Most importantly, a new index called clonic convulsion rate, combined with mortality was used to evaluate the toxicities of Apl on zebrafish larvae. We found that Apl can induce deformity and cardiovascular toxicity in both zebrafish embryos and larvae. This microdevice is a multiplexed testing apparatus that allows for the examination of indexes beyond toxicity and teratogenicity at the sub-organ and cellular levels and provides a potentially cost-effective and rapid pharmaceutical safety assessment tool.

Chromosome aberrations induced by clinical medicines

Inducibility of chromosome aberrations of cultured mammalian cells was examined on 11 clinical medicines which are used for a long term mainly in the field of internal medicine. P-aminosalicilic acid, isonicotinic acidhydrazid, streptomycin A, hydralazine hydrochloride methimazole and theophylline induced definite increase of chromosome aberrations. Among them P-aminosalicilic acid was a little weak in its effect. The effects of rifamycin SV, aminophylline and isosorbide dinitrate were judged as suspicious, because only a slight increase of the aberrations were caused. Reserpine and propylthiouracil induced little chromosome aberrations. Effective concentrations of these medicines in our chromosome test were compared with their maximum blood concentrations in clinical use in human quoted from the published papers. Their ratios by isonicotinic acid hydrazid, streptomycin A, methimazole, theophylline and issorbide dinitrate were very high and those by others were relatively low. Because p-aminosalicilic acid, rifamycin SV, hydralazine hydrochloride and aminophylline were positive or suspicious in our chromosome test, further pursue for the safety evaluation seems necessary.

Aminophylline exhibits convulsant action in rats during ontogenesis

Aminophylline-induced seizures were studied in 166 male albino rats in five age groups--7, 12, 18, 25 and 90 days old. Aminophylline injected in doses from 150-350 mg/kg i.p. elicited both minimal, clonic and major, i.e. generalized tonic-clonic seizures during the 60-min observation period. The pattern of minimal seizures did not change during development; major seizures exhibited changes in proportion to their three phases--running, tonic and clonic phases. Dependence on the dose of aminophylline was observed in the incidence of major seizures as well as in shortening of latencies of both types of seizures. More marked convulsant effects of aminophylline in 7-, 12- and 18-day-old rat pups than in older animals might be due to pharmacokinetic as well as pharmacodynamic factors.

Dose-finding study with nimodipine: a selective central nervous system calcium channel blocker on aminophylline induced seizure models in rats

Nimodipine, a dihydropyridine derivative central nervous system (CNS) selective calcium channel blocker was studied at four different dosage schedules in five different models of seizures in rats. At a dose of 5 mg/kg, i.p. with pretreatment time of 15 min, nimodipine significantly antagonized aminophylline (175 and 200 mg/kg, i.p.), electroshock (150 mA for 0.2 s), pentylenetetrazole (60 and 75 mg/kg, i.p.), aminophylline (100 mg/kg i.p.) + electroshock (66mA for 0.2 s), and aminophylline (100 mg/kg, i.p.) + pentylenetetrazole (40 mg/kg, i.p.) induced seizures in rats. No hemodynamic alteration was observed with this dose of nimodipine. However, 2 mg/kg, i.p. (pretreatment time of 15 min and 30 min) and 5 mg/kg, i.p. (pretreatment time of 30 min) doses of nimodipine failed to demonstrate any significant anticonvulsant effect. The study highlighted the critical role of calcium ion flux into the neurons for the genesis of seizure activity to aminophylline, electroshock, and pentylenetetrazole in rats. Furthermore, the critical dose requirement for nimodipine could be explained on the basis of its short half-life and shorter duration of protection against seizures. Therefore, nimodipine may be tried clinically as an anticonvulsant in patients who are on aminophylline because of bronchial asthma or chronic obstructive pulmonary disease, when such patients have concomitant epilepsy or other seizure prone neurological deficits or are scheduled to undergo electroshock therapy.

Role of alpha- and beta-adrenergic activation in ventricular fibrillation death of corticoid-pretreated rats

Death in ventricular fibrillation was induced consistently in desoxycorticosterone acetate-pretreated rats by the beta-adrenergic agonist isoproterenol but not by norepinephrine or epinephrine, both of which possess alpha- as well as beta-adrenergic activity. Aminophylline, which enhances beta-adrenergic activity, and phenoxybenzamine, an alpha-receptor blocking agent, were used to study the roles of alpha- and beta-adrenergic stimulation in the production of ventricular fibrillation. With the addition of aminophylline, both norepinephrine and epinephrine produced death in ventricular fibrillation, and the existing cardiotoxicity of isoproterenol was potentiated. Similarly, in the presence of phenoxylbenzamine, doses of norepinephrine and epinephrine that had been well tolerated became lethal. Internventions that favor beta-adrenergic preponderance, either by enhancing beta-effects or by blocking protective alpha-adrenergic activation, apparently increase the arrhythmogenic propensity of norepinephrine and epinephrine in steroid-pretreated rats. The similarity of some forms of stress to the experimental protocol of chronic steroid treatment followed by acute catecholamine exposure is discussed.

Comparative toxicity of caffeine and aminophylline (theophylline ethylenediamine) in young and adult rats

The toxicity of aminophylline and caffeine was studied in adult and 2-day-old rats following a single subcutaneous injection of the respective drug. Following the injection of high doses of either methylxanthine, adult rats developed convulsions, tremors, lethargy and licking of lips. In adult rats, the LD50 of caffeine and aminophylline was the same after 24 h and after 1 week of observation: caffeine 265 mg/kg, and aminophylline 202 mg/kg (theophylline base 172 mg/kg). In young rats, the LD50 was greater when the observation was carried out for 1 week than at 24 h after the injection; at 24 h: caffeine 220 mg/kg, and aminophylline 169 mg/kg (theophylline base 144 mg/kg); at 1 week: caffeine 155 mg/kg, and aminophylline 140 mg/kg (theophylline base 119 mg/kg). Young rats failed to gain weight at a normal rate after administration of either methylxanthine. The greater toxicity of both methylxanthines in newborn animals may be at least partly due to the extremely slow elimination of theophylline and caffeine in the neonate.

Proconvulsant effect of aminophylline on cortical epileptic afterdischarges varies during ontogeny

Effect of aminophylline on epileptic afterdischarges (ADs) induced repeatedly by rhythmic electrical stimulation of sensorimotor cortical area was studied in rat pups 12, 18 and 25 days old. The proconvulsant effect of aminophylline (50 and/or 100 mg/kg i.p.) was more expressed in 12- and 18-day-old rats than in the oldest group. In 12-day-old rat pups there was an enormous increase of transition of the spike-and-wave type of ADs into the second, limbic type, a situation observed only exceptionally under control conditions. A prolongation of ADs was related to this transition (limbic ADs are always longer than spike-and-wave ones). Eighteen-day-old rats exhibit this transition less frequently but a marked prolongation of spike-and-wave ADs was recorded in a part of these animals forming a pattern of status lasting some tens of minutes. Aminophylline led only to a transient prolongation of spike-and-wave ADs in the oldest group. The transition into the limbic type of ADs was seen in this age group only exceptionally what is in contrast to age-matched controls in which this transition is common. The effect of aminophylline on cortical ADs which is most marked in the youngest group changes qualitatively during postnatal development.

Diazepam-atenolol combination antagonizes aminophylline-induced convulsions and lethality in mice

The present study was undertaken to identify protective drugs against aminophylline (240 mg/kg i.p.)-induced convulsions and lethality in mice. Diazepam (10 mg/kg) and valproic acid significantly prevented the convulsions, but were not effective in preventing mortality. Phenytoin, atropine, carbamazepine and atenolol were ineffective in protecting against convulsions and death. Ketamine gave partial protection against convulsions, but was not effective in preventing mortality. Diazepam (10 mg/kg) and atenolol (5 mg/kg) administered together gave total protection against convulsions and death. These results show that aminophylline-induced convulsions are relatively resistant to antiepileptic drugs, and that a combination of diazepam and a beta-blocker (atenolol) has potential as an anti-aminophylline agent.

Oral sustained-release aminophylline in medical inpatients: factors related to toxicity and plasma theophylline concentrations

1 Consecutive medical inpatients expected to benefit from a theophyllinate were treated with sustained-release aminophylline in a protocol conforming with ordinary practice. Of 16 patients, five had toxicity with aminophylline 450 mg daily, and a further three with 900 mg daily. Toxicity was serious in three patients. 2 Toxicity was significantly less common in cigarette smokers, and was related to higher plasma theophylline concentrations. However, there was a large overlap between concentrations associated with toxicity (as low as 9 micrograms/ml) and the accepted therapeutic range (5-20 micrograms/ml). Most patients with toxicity had theophylline levels within the therapeutic range. 3 For the same dose of aminophylline there was sevenfold variation between patients in plasma theophylline, with higher concentrations in non-smokers, infrequent alcohol users, older patients, those with left ventricular failure and those with lower serum transaminases. There variables could not be separated completely because of the small number of observations. 4 A nomogram for aminophylline dosage or monitoring of serum theophylline levels would have prevented little of the toxicity observed in these patients, although these measures would ensure that therapeutic concentrations were attained, and might prevent life-threatening toxicity.

Toxicity and tissue distribution of aminophyline in neonatal and adult mice and rats

The LD50 of aminophylline in adult mice differed from young mice and rats of both ages, in which the values were remarkably similar (Table 1). With the exception of fat, which had lower concentrations in all groups, tissue concentrations after a 4 mg/kg rectal dose of aminophylline in the 10-day-old animals ranged from 10-20 microng/g as compared to 4-10 microng/g in the adults (Table 2). To evaluate preferential distribution, an analysis of tissue to blood concentration ratios was made. All ratios approximated 1.0 except fat which had a ratio of 0.1-06. The neonates of each species had significantly higher tissue to blood ratios for brain, heart, small intestine, skeletal muscle, and fat (P less than 0.05). Brain to plasma and brain to blood ratios were very similar ranging from 0.4-1.3 in adults versus 0.8-1.7 in neonates. Consideration of the time course indicated a trend toward unit, with the overall ratio in both groups being 1.15 at 2 hr. However, at all earlier time periods the ratios were clearly higher in neonates. Administration of aminophylline intraperitoneally to produce serum concentrations of theophylline far in excess of the 10-20 microng/ml considered to be safe and effective in clinical use did not decrease bilirubin levels in young or old Gunn rats (Fig. 1).

Search for an antidote to electroconvulsion and lethality in aminophylline-sensitized mice

Diazepam (10 mg/kg i.p.) or MK-801 (0.25 mg/kg i.p.) offered complete protection against corneal electroshock (30 mA x 0.2 s)-induced tonic seizures and lethality but failed to protect from aminophylline (150 mg/kg i.p.) + electroshock (15 mA x 0.2 s)-induced tonic seizures and lethality in mice. The diazepam (2.5 mg/kg i.p.) and MK-801 (0.25 mg/kg i.p.) combination completely protected the mice from aminophylline + electroshock-induced seizures and lethality. Sodium valproate (500 mg/kg i.p.) protected the mice from electroshock (30 mA) per se and aminophylline + electroshock (15 mA)-induced seizure and lethality. The present study established the neurosensitizing potential of a single, non-convulsive dose of aminophylline for electroconvulsion due to subthreshold intensity electroshock and demonstrated the prophylactic efficacy of sodium valproate and the synergistic therapeutic potential of diazepam and MK-801 combination against such seizure attacks.

Aminophylline aggravates long-term morphological and cognitive damages in status epilepticus in immature rats

Here, we investigated whether aminophylline, an adenosine receptor antagonist used usually as a treatment for premature apnea, had synergistic effects on status epilepticus in the developing brain. On postnatal day 14 (P14), four groups of rats intraperitoneally received saline, aminophylline, lithium--pilocarpine (Li-PC), and Li-PC plus aminophylline, respectively. Subsequently, the Morris water maze task was performed at P80. The brains were then analyzed with cresyl violet stain for histological lesions and evaluated for mossy fiber sprouting with the Timm stain. No seizures were elicited in the saline-treated or aminophylline-treated rats. Both the Li-PC-treated and aminophylline plus Li-PC-treated rats exhibited seizures and there was no significant difference in mortality between the two groups. More interestingly, as in adulthood (P80), aminophylline aggravated the spatial deficits and histological damages seen in Li-PC-treated rats. In summary, this present study suggests that the use of adenosine receptor antagonists, such as aminophylline, exacerbates seizure-induced damage in the developing brain.

Effect of aminophylline on transpulmonary passage of venous air emboli in pigs

Aminophylline has been shown to dramatically reduce the filtering capacity of the lung in dogs during venous air embolism. Similarities have been pointed out between the cardiovascular and respiratory systems of the pig and of humans. We therefore wanted to find out whether aminophylline also modifies the transpulmonary spillover of microbubbles to the arterial circulation of the pig. Twenty-eight pigs were anesthetized with pentobarbital sodium and mechanically ventilated. Aminophylline was injected intravenously into 10 of the pigs before the introduction of air bubbles into the right ventricle, while the other 18 pigs served as controls. A transesophageal echocardiographic probe was used to detect eventual air bubbles in the left atrium or in the aorta. Pigs received either air infusion, at rates varying from 0.05 to 0.20 ml.kg-1.min-1, or calibrated microbubbles, 5-300 microns diam. We found that aminophylline-treated pigs did not show any change in spillover incidence compared with controls. Furthermore, in both groups the spillover during continuous air infusion seemed to be a preterminal event, because the pigs had very low arterial pressure when arterial bubbles were observed. Finally, there was an increase in mean pulmonary arterial pressure from 18 +/- 3.4 to 26 +/- 2.2 (SD) mmHg (n = 4, P less than 0.01) in aminophylline-treated pigs after a bolus injection of microbubbles (less than or equal to 50 microns, total volume less than 0.5 ml). Our results suggest that aminophylline does not modify the transpulmonary passage of microbubbles in this porcine model. In addition, it would seem that the pulmonary circulation of the pig is sensitive to very small volumes of air, when injected as microbubbles.